This invention relates to a process for producing an .alpha.,.beta.-unsaturated carbonyl compound. More particularly, it relates to a process for producing an .alpha.,.beta.-unsaturated carbonyl compound useful for production of chemical substances such as medicines, agricultural chemicals, perfumes, etc., by the reaction of an alkenyl ester and an allyl type carbonic ester. The invention is also directed to purification of such an .alpha.,.beta.-unsaturated compound.
.alpha.,.beta.-unsaturated carbonyl compounds such as 2-cyclopentenone, 2-cyclohexenone, 2-cyclododecenone, etc. are very useful chemical substances in the fields of medicines, agricultural chemicals, perfumes, etc.
As a process for synthesizing such an unsaturated carbonyl compound, there has been reported a process which comprises treating an alkenyl ester and an allyl type carbonic ester with a platinum group metal compound catalyst in the presence of an organotin alkoxide (Jap. Pat. Appln. Kokai (Laid-Open) No. 60-36435, and Chemistry Letters 1133-1136 (1984)). However, the organotin alkoxide used as indispensable component in this process is difficult to handle and it is insufficient in safety from the viewpoint of industrial hygiene and contamination of the organotin alkoxide to a final product.
As a process for producing such an .alpha.,.beta.-unsaturated carbonyl compound, there has been known, for example, a process which comprises reacting, as illustrated by the formula shown below, an alkenyl ester such as 1-cyclopentenyl acetate with an allyl type carbonic ester such as allyl methyl carbonate in the presence of a platinum group metal compound catalyst. ##STR3##
This process uses easily available compounds as starting materials and permits relatively efficient production of an .alpha.,.beta.-unsaturated carbonyl compound. However, it requires selective separation and purification of the reaction product, i.e., the .alpha.,.beta.-unsaturated carbonyl compound because the actual reaction mixture contains unreacted allyl type carbonic ester and an allyl acetate by-product in addition to the .alpha.,.beta.-unsaturated carbonyl compound.
For reducing the amount of the residual starting allyl type carbonic ester in the reaction mixture, reduction of the amount of the allyl type carbonic ester used may be considered. However, reduction of the allyl type carbonic ester is substantially impossible because for producing the .alpha.,.beta.-unsaturated carbonyl compound, it is essential to use an amount of the allyl type carbonic ester which is equivalent to or larger than the amount of the alkenyl ester. Therefore, the presence of unreacted allyl type carbonic ester in the reaction mixture is unavoidable.
On the other hand, as a method for the separation and purification of the .alpha.,.beta.-unsaturated carbonyl compound from the reaction mixture, purification by distillation may be considered at first. However, when the boiling point of the unreacted, residual allyl type carbonic ester is close to that of the desired product, i.e., the .alpha.,.beta.-unsaturated carbonyl compound, they cannot be separated from each other by distillation. Therefore, a method is required by which the .alpha.,.beta.-unsaturated carbonyl compound can be separated efficiently in high purity by a means other than distillation.
As information concerning a method for this separation, it has been reported that allyl carbonate can be decomposed by reacting triphenylphosphine and palladium acetate with allyl carbonate in the molar ratio of triphenylphosphine/palladium acetate=5 with heating [Tetrahedron Letters, 12, 3591 (1981)]. However, close investigation by the present inventors proved that allyl acetate by-product could not be decomposed by such a method.
In addition, the by-product allyl acetate can be decomposed by hydrolysis with a strong acid or a strong alkali or by heating at a high temperature, but when such a decomposition method is applied to a reaction system for producing the .alpha.,.beta.-unsaturated carbonyl compound, decomposition of the desired .alpha.,.beta.-unsaturated carbonyl compound is inavoidable.
Accordingly, it has been very difficult to separate and purify the .alpha.,.beta.-unsaturated carbonyl compound efficiently in high purity from the reaction mixture obtained by the reaction of the alkenyl ester with the allyl type carbonic ester, by a heretofore known method.